The Avalanche, who have lost two games in a row and four of their past five, are five points behind the Minnesota Wild for the second wild card into the playoffs from the Western Conference with four games remaining, one more than the Wild.
Colorado would be eliminated with a regulation loss if the Wild defeat the Winnipeg Jets on Sunday.
"We have nothing to lose at this point," Avalanche center Matt Duchene said. "I think we almost have to think like that. That's not saying we play loose and careless, it's playing confident and on our toes and just go for it at this point. We don't want to have any regrets.
"It's frustrating to be in the position we're in, but we have four games (left) and we'll make the best of it. At the very least we have to play for our fans and the logo, finish hard."
Avalanche goalie Semyon Varlamov will make his sixth consecutive start.
The Blues, who have a clinched a playoff berth, are in second place in the Central Division, four points behind the Dallas Stars with four games left, one more than the Stars. They are four points ahead of the Chicago Blackhawks.
St. Louis is coming off a 6-5 loss to the Boston Bruins on Friday that ended their winning streak at five games.
Jake Allen stopped four of five shots after relieving Brian Elliott to begin the third period Friday and will start Sunday. Allen has gone 7-1-0 in his past nine starts.
The Avalanche and Blues didn't have morning skates Sunday.
Here are the projected lineups:
BLUES
Alexander Steen - Jori Lehtera - Vladimir Tarasenko
Jaden Schwartz - Paul Stastny - Troy Brouwer
Dmitrij Jaskin - Patrik Berglund - David Backes
Scottie Upshall - Kyle Brodziak - Ryan Reaves
Joel Edmundson - Alex Pietrangelo
Kevin Shattenkirk - Colton Parayko
Petteri Lindbohm - Robert Bortuzzo
Jake Allen
Anders Nilsson
Injured: Jay Bouwmeester (upper body), Robby Fabbri (lower body), Carl Gunnarsson (lower body), Steve Ott (hamstring)
Scratched: Brian Elliott, Magnus Paajarvi
AVALANCHE
Mikkel Boedker - Matt Duchene - Mikhail Grigorenko
Gabriel Landeskog - Carl Soderberg - Blake Comeau
Shawn Matthias - John Mitchell - Jarome Iginla
Cody McLeod - Andrew Agozzino - Jack Skille
Chris Bigras - Erik Johnson
Nick Holden - Tyson Barrie
Zach Redmond - Francois Beauchemin
Semyon Varlamov
Calvin Pickard
Injured: Eric Gelinas (elbow), Nathan MacKinnon (knee), Brad Stuart (back surgery), Jesse Winchester (head), Nikita Zadorov (concussion)
Scratched: Andrew Bodnarchuk, Andreas Martinsen
Status report: Bouwmeester, Fabbri and Gunnarson have resumed skating and are expected to return this week. Elliott didn't accompany the Blues for the one-game trip. ... Redmond is expected to replace Zadorov, who was injured Friday against the Washington Capitals.
Who's hot: Stastny has one goal and six assists in a four-game streak, Tarasenko has two goals and two assists in a four-game streak and Backes has one goal and three assists in a three-game streak. ... Landeskog has two goals and one assist in the past three games, Comeau has one goal and two assists in three games and Soderberg has three assists in three games.
